Add #zoomFactor= method
prepare PR

* require setter attribute
* add CHANGELOG record
Merge pull request #428 from budnik/zoom-factor

add page.zoomFactor=
Fixed #432, setting multiple contenteditables.

It seems that if something else has the input focus when we call `set`
on a `contenteditable`, the wrong text is deleted. By clicking on the
`contenteditable` first, we ensure we'll delete the right text.
Better fix for #432, setting contenteditable.

deleteText was deleting the wrong text, not because the focus was
on another element, but because previously selected text was still
selected. Now we clear the selection before adding the new text to
it.
Merge pull request #433 from eostrom/master

Fixed #432, setting multiple contenteditables.
Log raw JSON messages/responses rather than Ruby-parsed and inspected

This allows problems to be more easily reproduced and also allows for
the logger output to be programatically parsed (by languages other than
Ruby).
Add JSON logging to the changelog